1. Technical Field
This application relates to the art of radio transmission devices in MHz (megahertz) band (e.g. 920 MHz).
2. Description of Related Art
With regard to the 920 MHz frequency band in Japan, the standard “ARIB STD-T108” (February 2012) was laid down and disclosed as an “ARIB STANDARD” by the ARIB (Association of Radio Industries and Businesses).
Conditions of a transmission stop in the 920 MHz band may be described as shown below in (A) to (C). That is, in the 920 MHz band, if a transmission by a given transmitter meets any of conditions (A) to (C), the transmission may be stopped or inhibited (e.g., delayed).
(A) A cumulative transmission period (e.g., accumulated transmission time) per unit time (e.g. one hour) would exceed a predetermined limit (e.g., 360 seconds).
(B) A transmission of one frame takes longer than a predetermined time period (e.g. 3 ms [channel width is 400 kHz (kilohertz)], 2 ms [channel width is 600 kHz to 1000 kHz]) to complete. Here, the stopping may take the form of a fixed idle or wait period (e.g., 2 ms) that is required before the transmitter is permitted to transmit again.
(C) A continuous period of transmission would exceed a maximum permitted continuous transmission period. For example, if before completing transmissions of all frames that would be requested by a destination, the end of a predetermined continuous period (e.g. 200 ms [channel width is 400 kHz], 100 ms [channel width is 600 kHz to 1000 kHz]) of transmission is reached, further transmission may be stopped or inhibited.
A simplified structure of a related art radio transmission device that would operate according to conditions (A) to (C) is shown FIG. 3.
Referring to FIG. 3, a radio transmission device 100 in the related art may include a transmission frame interface module 101, a frame transmitting module 102 that sends transmission frames, a stop condition checking module 103, and an upper layer processing module 104. The transmission frame interface module 101 sends transmission frames to the upper layer processing module 104, or it receives transmission results from the upper layer processing module 104. The stop condition checking module 103 judges whether any of conditions (A) to (C) is met. The upper layer processing module 104 performs processes of an upper layer that includes the network layer and the application layer, and so on. The lower layer processing module 105 includes the transmission frame interface module 101, the frame transmitting module 102, and the stop condition checking module 103. The lower layer processing module 105 performs processes of a lower layer that has the MAC (Media Access Control) layer or the PHY (physical) layer. The MAC layer is generally called the data link layer.
A request for frames from the upper layer processing module 104 is transmitted to the frame transmitting module 102 via the transmission frame interface module 101. Then, the stop condition checking module 103 checks whether any of conditions (A) to (C) is met. If a condition is met, the stop condition checking module 103 instructs the frame transmitting module 102 to stop transmitting. The frame transmitting module 102 sends the frames according to the instruction from the stop condition checking module 103. That is, when there is no instruction to stop transmission from the stop condition checking module 103, the frame transmitting module 102 continues transmitting the frames. But, if there is an instruction to stop transmission from the stop condition checking module 103, the frame transmitting module 102 suspends transmitting the frames. The frame transmitting module 102 sends a transmission result to the upper layer processing module 104 via the transmission frame interface module 101.
One or all of the processes that are conducted by the lower layer processing module 105 in the MAC layer may be achieved by one or more computer programs (e.g., a MAC layer program). In this case, a MAC layer program of the lower layer processing module 105 generally returns a transmission error, if one of the conditions is met and transmission is stopped, to the upper layer processing module 104 without conducting transmission during the stopping of transmission.
However, the upper layer processing module 104 doesn't distinguish whether condition (A), condition (B) or condition (C) is the primary cause of transmission error. As a result, the upper layer processing module 104 treats them as the same error. This results in some problems, as described hereinafter.
When the primary cause of the transmission error is condition (B), the idle period of 2 ms must pass before the MAC layer program is able to transmit again. But this may cause the transmission rate to go down, because the MAC layer program must inform the upper layer processing module 104 of the transmission error, and then it must transmit again.
When the primary cause of the transmission error is condition (A), the MAC layer program is not able to transmit again until the next period of time to measure. Moreover, the upper layer processing module 104 is not able to know the time when the next period of time to measure will come.
When the primary cause of the transmission error is condition (C), the upper layer processing module 104 doesn't know how to process after the transmission error, because the upper layer processing module 104 doesn't know the cause for the transmission error.